Martial arts training is more fun and productive when training with a good partner. A good partner can help enhance your skills in ways not possible if alone.
Unfortunately, good training partners are hard to find (or perhaps are less memorable). Instead,
Here is a list of the worst type of training partners encountered on the training grounds.
The whiner

You stop your fist before you touch him, he claims you never could have touched him; You touch him, he claims your hit was inoffensive; You hit him harder, he reminds you that its a light sparring session and that he also can hit you hard; You disregard his warning and keep hitting him and he’ll go into great length explaining how a bad night of sleep / heavy meal / any unusual occurrence in his life is hindering his performance and how on any other day, he would overpower you.
The undercover-teacher

Sent from the master organization somewhere in the mountains of Asia, his mission is to oversee the sensei's teaching quality. He may be no better than you or sometimes, even below your skill level, yet, he will always have comments on how your techniques are wrong and will readily give you tips to improve. During the whole training session, he will pay a lot more attention to your technique than he will of his own.
They often use secret vestimentary codes in order to recognize people of their society, most often in the form of a green belt.
The water elemental

The water elemental (a.k.a heavy sweater) is best to be avoided when practicing a grappling sport, like Brazilian Ju-jitsu or wrestling. It is not so much because the fluids make him slippery that you want to avoid him but rather because he is downright disgusting. Could you imagine being under his dripping wet body during a ground exercise? If that happens to you, better keep your mouth closed.

Remeber to keep your mouth closed... or else...
Photograph by Nicole-Koehler, via Wikimedia Commons
And if you think practicing a contact sport will prevent sweat from transfering to you, do know that some people have (unwillingly) mastered the art of throwing sweat balls...

The water conservationist

The water saver believes in water conservation. In order to save water consumption, he will wear his training clothes for more sessions before dumping it in the washing machine. This would not be much of a big deal if your nose was congestioned by flu and you couldn’t smell anything, but for all the times you were healthy, the putric smell is more than the toughest guy in class could handle. Your only hope, if sparring with the water saver is to hold your breath and beat him before you pass out from lack of oxygen. You would have passed out he you breathed anyways...
The gas man
The gas man, as his name implies, uses gas composed of nitrogen, hydrogen, carbon dioxyde, oxygen and methane as a secret weapon... need I say more?

If his submission move doesn't work, then he will go for the armbar...
The wolverine

This partner does not believe in trimming finger and toe nails. That’s pretty much like attaching mini daggers to their toes and fingers. When they kick, it is best not to block as blocking the kick will not guarantee you won’t get a nasty cut form the kick. And by judging from the looks of those toe nails, that cut probably propagated deadly bacterias to your freshly cut wound.
The cactus man

Photograph taken from Daniel White http://www.advancedphotoshop.co.uk/show_image.php?imageID=40799
Similar to the wolverine except his weapons are in the form of spikes and are located on his face, in the form of very short beard. Probably an excellent defense against choke holds as any neck choke attempt will result in bloody forearms for the attacker.
Reading that may interest you
- 11 steps to deal (and learn) with criticism
- 11 reasons why it sucks to be a martial arts sensei, instructor, coach or teacher
- Don Cunningham: The dangers of Martial Arts self proclaimed masters
- Green belts know everything -- even the family secret recipe
- 6 Reasons why I rather keep my training a secret